1. Field of the Invention
Aspects of the present invention relate to an organic light emitting diode (OLED) display device and a method of fabricating the same and, more particularly, to an OLED display device, and a method of fabricating the same, in which a metal catalyst remaining in a channel region of a semiconductor layer crystallized using the metal catalyst is gettered so that the amount of metal catalyst remaining in the semiconductor layer is reduced so as to improve the electrical properties of the OLED display device.
2. Description of the Related Art
In general, a polycrystalline silicon (poly-Si) layer is widely used as a semiconductor layer for a thin film transistor (TFT) because the poly-Si layer has high field-effect mobility, is applicable to a high-speed operating circuit, and may be used to configure a complementary-metal-oxide-semiconductor (CMOS) circuit. A TFT using the poly-Si layer typically functions as an active device of an active-matrix liquid crystal display (AMLCD) or a switching device or a driving device of an organic light emitting diode (OLED).
Methods of crystallization of an amorphous silicon (a-Si) layer into a poly-Si layer include a solid phase crystallization (SPC) method, an excimer laser annealing (ELA) method, a metal induced crystallization (MIC) method, and a metal induced lateral crystallization (MILC) method.
Specifically, the SPC method includes annealing an a-Si layer for several to several tens of hours at temperatures below about 700° C. as a glass substrate for a display device using a TFT is deformed at temperatures above about 700° C. The ELA method includes partially heating an a-Si layer to a high temperature in a short amount of time by irradiating excimer laser beams to the a-Si layer. The MIC method includes bringing a metal, such as nickel (Ni), palladium (Pd), gold (Au), or aluminum (Al), into contact with an a-Si layer or injecting the metal into the a-Si layer to induce phase transition from the a-Si layer to a poly-Si layer. Also, the MILC method includes sequentially inducing the crystallization of an a-Si layer while laterally diffusing silicide formed by reaction of the metal with the silicon.
However, since the SPC method involves annealing a substrate at a high temperature for a long period of time, great damage may occur to the substrate. Also, the ELA method not only requires expensive laser apparatuses but also causes protrusions on the surface of the poly-Si layer so as to degrade interface characteristics between a semiconductor layer and a gate insulating layer. Furthermore, according to the MIC or MILC method, a large amount of metal catalyst may remain in a poly-Si layer, thereby increasing the leakage current of a semiconductor layer of a TFT.
Nowadays, a vast amount of research is being conducted on methods of crystallizing an a-Si layer using a metal catalyst because the a-Si layer may be crystallized at a lower temperature for a shorter amount of time than in the SPC method. Typical methods of crystallizing an a-Si layer using a metal catalyst include an MIC method, an MILC method, and a super grain silicon (SGS) method. In these methods, however, the device characteristics of a TFT may be degraded due to contamination caused by the metal catalyst.
In order to prevent contamination caused by a metal catalyst, after an a-Si layer is crystallized using the metal catalyst, a gettering process may be performed to remove the remaining metal catalyst. Conventionally, the gettering process is performed using impurities, such as phosphorus (P) gas or a noble gas, or by forming an a-Si layer on a poly-Si layer. However, in the conventional methods, the metal catalyst is not effectively removed from the poly-Si layer, and a problematic leakage current still remains.